The undated microscope picture shows a plankton group three weeks after its fertilisation with iron on the research vessel Polarstern. Photograph: Philipp Assmy/EPA

Seeding the oceans with iron is a viable way to permanently lock carbon away from the atmosphere and potentially tackle climate change, according to scientists who have studied how the process works naturally in the ocean.

The study, from researchers at the University of Southampton, is published following the announcement earlier this week that scientists from the Alfred Wegener Institute in Germany were finally given the go-ahead for a controversial experiment to drop several tonnes of iron into the Southern Ocean. Some environmentalists are concerned that the long-term ecological effects of iron seeding are unknown.

Ocean geo-engineering using iron as a fertiliser for microscopic creatures in the ocean is seen as a possible way to slow down global warming. Marine algae and other phytoplankton capture vast quantities of carbon dioxide from the atmosphere as they grow, but this growth is often limited by a lack of essential nutrients such as iron. Artificially adding these nutrients would make algae bloom and, as the organisms grow, they take up CO2. When they die, some of the organisms sink to the bottom of the ocean, taking their carbon with them. But there has been little scientific work previously on whether the CO2 stays locked up for a significant period of time.

Understanding how much iron is needed, how it should be added and what effect it would have on the local ecology is crucial in assessing whether iron fertilisation would be a useful tool in reducing carbon dioxide in the atmosphere.

In the latest research, published tomorrow in Nature, the Southampton scientists studied a natural source of iron into the sea near the Crozet Islands at the northern boundary of the Southern Ocean, 1,400 miles south-east of South Africa. Their work showed that iron – which is added by the volcanic rocks to the north but not to the south of the island – successfully tripled the growth of phytoplankton and also the amount that sank to the bottom of the sea.

Peter Burkill, director of the Sir Alister Hardy Foundation for Ocean Sciences in Plymouth, said: "This is a significant result. It suggests that ocean iron fertilisation might work for reducing atmospheric CO2 through export of carbon into the ocean's interior. But the next step from natural experiments, such as this one, to artificial ones is crucial. We now need to know what the ecological impacts of artificial fertilisation experiments are."

Andrew Watson of the University of East Anglia, said that previous small-scale artificial ocean fertilisation experiments had already shown that plankton are stimulated by iron, but there had long been questions about how deep the carbon is sequestered. "This paper suggests that Southern Ocean iron fertilisation can be quite effective at sending the carbon into the deep ocean."

The Southampton study also made progress in understanding how iron fertlisation might work best. Their work showed that the amount of carbon that sank per unit of iron added, called the downward flux, was 77 times lower around Crozet than the flux measured in the only other survey of a natural iron source, carried out several years ago by French scientists in the Kerguelen Islands in the Southern Ocean.

Richard Sanders of the University of Southampton, who took part in the study, said that the difference in algal blooms between different locations might be a result of several factors, including the type of iron compound used and also how it gets into the water. Around the Kerguelen Islands, the iron source comes from the relatively shallow sea floor. "Around the Crozet islands the iron seems to be coming in horizontally. It's possible that iron that comes off the land in this manner is different in some way," said Sanders. In addition, the Crozet iron is mainly in the form of small rock particles that do not dissolve in the water.

Sanders says that the results have implications for the way iron-seeding experiments might be carried out in the future. For a start, they would probably require more iron than previously thought for any serious geo-engineering purpose and the compounds they choose to drop into the sea would need to be carefully chosen so that they stayed in the water long enough to take effect, rather than simply sinking straight to the bottom.

Later this year, the team from the Alfred Wegener Institute will go out on the Polarstern research ship to examine some of these questions. They plan to place several tonnes of iron sulphate onto the surface of the Southern Ocean , primarily to study the role of iron in the biochemistry of the ocean. Karin Lochte, director of the institute said that its project would "help in arriving at a substantiated and fact-based political decision on whether or not iron fertilisation in the ocean is a useful technique that could contribute to climate protection."

Watson said: "It's interesting that [the Polarstern] has been at the centre of a lot of controversy because they wanted to do an artificial experiment with 10 or 15 tonnes of iron. As this [Southampton] paper shows, much larger amounts of iron are being added daily by natural processes around the Crozet Island, and it doesn't seem to have done the Antarctic ecosystem any harm."